After five years in the SBS, Stonebridge was personally selected by Colonel Grant to join the elite special operations unit; Section 20.
Michael's immediate family are all deceased; his father was a Royal Marine like himself, however his father was killed during the Falklands War. His mother left two years after his father passed away.
Stonebridge joined the Royal Marines at the age 18. He also had a wife; Kerry however she was killed by Craig Hanson; he wanted revenge because Michael killed his brother; Jake Hanson after Jake went rogue on a SBS training exercise.